104 
There is another great difficulty yet to be overcome be- 
fore the artificial alizarine can become a commercial article, 
that is, the obtaining of anthracene in larger quantities, and 
this question is of some importance to us: England being 
the great tar producing country. Anthracene does not appear 
to exist in greater proportion than one in a thousand of tar, 
and is only liberated or produced during the latter part of 
the distillation of the tar. In fact if the distillation be 
stopped so as to leave a very soft pitch, the oils obtained give 
little or no anthracene. If on the other hand it is carried on 
so as to get 10 or 15 per cent, more oil off, there remains a 
hard pitch which has little or no value at the present day, 
the quantity of anthracene obtained varying very much 
according to the nature of the coals employed in the pro- 
duction of the tar, ranging from 1 J to 8 per cent, of the 
heaviest oils separated; it will scarcely be worth the while 
of the tar distiller to depreciate the value of one of the 
staple articles of his trade to produce it, and even when the 
heavy oil is obtained the separation of the small quantity 
of anthracene it contains, and its purification for use accor- 
ding to the above patents will yet require much time and 
research. It is well known to all who have worked 
on the coal-tar products that each well defined compound 
is mixed with homologues which renders its separation and 
purification a work of extreme difficulty, thus aniline is 
mixed with picoline and several other alkaloids, benzol with 
toluol and other hydrocarbons, carbolic acid with cresylic 
and other acids, and anthracene is also mixed in a similar 
manner with homologous compounds. 
The mere distillation and filtration of the solids obtained 
and their hot or cold pressing or even their sublimation, 
do not effect the complete purification of the substance. The 
purest product I have been able to obtain on a moderate 
commercial scale has contained, when cold pressed about 
40 per cent, and when hot pressed about 70 per cent of 
